延迟启动Docker服务，直到MongoDB在不修改Dockerfile的情况下运行

Question

我的docker-compose.yml中有两项服务。使用MailHog和MongoDB进行存储的邮件服务。

问题在于，在MailHog之前，MongoDB服务需要启动并运行。否则，MailHog将回退并使用其内存存储。

简单的depends_on是不够的，因为MongoDB服务需要一些时间才能启动。

[我知道wait-for-it等脚本，但是它们都需要修改Dockerfile，在本例中，我使用的是未经修改的MailHog Docker镜像。

是否有任何“内置”机制或解决方法，可以在MongoDB准备就绪之前将邮件服务延迟？

mail:
  image: mailhog/mailhog:v1.0.0
  deploy:
    restart_policy:
      condition: on-failure
      delay: 10s
      max_attempts: 3
      window: 60s

mail-db:
  image: mongo:4.2.6
  environment:
    MONGO_INITDB_DATABASE: mailhog
    MONGO_INITDB_ROOT_USERNAME: root
    MONGO_INITDB_ROOT_PASSWORD: root
  ports:
    - 27017
  deploy:
    restart_policy:
      condition: on-failure
    resources:
      limits:
        cpus: "0.5"
        memory: 500M

Answer 1

一种方法是提供自己的entrypoint脚本，您可以将其与volumes添加到容器中。在脚本中，等待与MongoDB的成功连接，然后执行原始入口点。

堆栈：

volumes:
  - /path/to/entrypoint.sh:/tmp/entrypoint.sh
entrypoint: /bin/bash
command: /tmp/entrypoint.sh

entrypoint.sh：

# Wait for service or whatever
exec /path/to/original/entrypoint

Answer 2

不，没有。但是，无需修改原始Dockerfile。您可以使用jwilder/dockerize（为此目的开发的工具（以及其他工具））extend。

FROM mailhog/mailhog:v1.0.0

# If required, you can change MONGOURL via docker -e [...]
ENV MONGOURL mail-db:27017

# The dockerize version used. You can set a different version with
# docker build --build-arg DOCKERIZE_VERSION=[...]
ARG DOCKERIZE_VERSION=v0.6.1

# Change to root to be able to install dockerize
USER root

# 1: Ensure the image is up to date, while we are at it
RUN apk update && apk upgrade \
# 2: Install curl and its dependencies as the virtual package ".deps"
&& apk add --virtual .deps curl \
# 3: Get dockerize
&& curl -L -O https://github.com/jwilder/dockerize/releases/download/${DOCKERIZE_VERSION}/dockerize-linux-amd64-${DOCKERIZE_VERSION}.tar.gz \
# 4: Unpack it and put it to the appropriate location as per FHS
&& tar -C /usr/local/bin -xzvf dockerize-linux-amd64-${DOCKERIZE_VERSION}.tar.gz \
# 5: Remove the tarball
&& rm dockerize-linux-amd64-${DOCKERIZE_VERSION}.tar.gz \
# 6: Cleanup
&& rm -rf /var/cache/apk/* \
# 7: Remove the virtual package ".deps"
&& apk del .deps

# Switch back to the user mailhog is supposed to run under
USER mailhog

# Run dockerize, which will start mailhog as soon as it was able to connect to $MONGOURL
ENTRYPOINT ["/bin/sh","-c","/usr/local/bin/dockerize -wait tcp://$MONGOURL MailHog"]
注意：无论出于何种原因，语法突出显示在Dockerfile上均无法正常工作

[使用以下docker-compose.yaml测试（deploy部分显然被docker-compose忽略了：]

version: "3"
services:
  mail:
    image: robertstauch/mailhog:v1.0.0-dockerized-v0.6.1
    build: .
    ports:
      - "8025:8025"
      - "1025:1025"
    deploy:
      restart_policy:
        condition: on-failure
        delay: 10s
        max_attempts: 3
        window: 60s

  mail-db:
    image: mongo:4.2.6
    environment:
      MONGO_INITDB_DATABASE: mailhog
      MONGO_INITDB_ROOT_USERNAME: root
      MONGO_INITDB_ROOT_PASSWORD: root
    deploy:
      restart_policy:
        condition: on-failure
      resources:
        limits:
          cpus: "0.5"
          memory: 500M